In wireless sensor networks, to save energy the nodes may perform a radio-frequency (RF) wakeup procedure, in which during a majority of the time the nodes are in a power down mode, and in which, periodically, the nodes wake up to sample the wireless channel for any signal, and if a signal is present they remain in an active mode to receive the message. In this regard, the signal may followed by a message, the type of which indicates the action or actions that are required to be performed by the awakened node after the wakeup, and in certain instances it may be essential that the type is known correctly by the awakened node before the actual packet exchange. Since a node may be simultaneously awakened by multiple nodes in the network, there is a chance that interference and/or collisions may occur.